The invention relates to a resonator filter comprising a housing structure, at least one resonator conductor in the housing structure, and a regulating means for regulating the frequency band of the resonator filter.
Resonator filters are used in base stations of mobile telephone networks, for example. In base stations, resonator filters can be used for instance as matching networks or filtering circuits in amplifiers of transceiver units. There are several different kinds of resonator filters, and a resonator usually comprises a housing or a body. Resonator filters comprising a housing structure are for instance a coaxial resonator filter or an LC filter. The housing structure of a resonator is made of metal. In coaxial resonator structures, for example, the housing structure encloses a conductor situated in the middle area of the cavity of the housing structure, this conductor being called a resonator or a resonator pin. Additionally, it is known to use so-called helix resonators, in which the resonator is formed of a helical resonator conductor.
The length of a resonator pin is generally equal to a fourth of the wavelength of a signal coming to the resonator or to half of said wavelength. For this reason, resonators are very practical in the microwave area. In solutions according to the prior art, the resonator is fastened to the bottom of the housing structure. In a solution, a regulating means implemented by a wire is fastened beside the fixing point of the resonator. The wire forms an inductive coupling. It has been possible to change the frequency band of the resonator by changing the length and the position of the wire.
In another prior art solution, the wire is fastened to the resonator. However, resonators according to the prior art show the problem that they are difficult to tune and regulate accurately to the correct frequency band in the mounting stage. In a further solution according to the prior art, soldering the wire in the resonator has led to tuning problems.